Adds Python Api for `ALS` under `ml.recommendation` in PySpark. Also adds seed as a settable parameter in the Scala Implementation of ALS.

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #6015 from brkyvz/ml-rec and squashes the following commits:

be6e931 [Burak Yavuz] addressed comments
eaed879 [Burak Yavuz] readd numFeatures
0bd66b1 [Burak Yavuz] fixed seed
7f6d964 [Burak Yavuz] merged master
52e2bda [Burak Yavuz] added ALS